1. Field of the Invention
The present invention relates to a small size electronic part such as, for example, an angular velocity sensor, acceleration sensor, mechanical filter, etc. to a small size electronic part having an electrode terminal output providing an electric signal and a method for manufacturing such and a method for forming a via hole for use in such a small size electronic part.
2. Description of the Related Art
Generally, an angular velocity sensor, acceleration sensor, mechanical filter, etc. is widely known as a small size electronic part produced by a silicon micromachining technique. Further, such a small size electronic part comprises, for example, a silicon substrate, and glass substrates which are bonded to the upper and lower surfaces of the silicon substrate, respectively. A functional element for detecting an angular velocity is formed in the silicon substrate, for example, and the functional element is sealed by the two glass substrates.
Such a conventional small size electronic part may be mounted on the surface of a circuit board. Further, in order to make the circuit board small-sized, it is required to reduce the mounting surface of the small size electronic part. To this end, there has been known a small size electronic part in which a via hole passing through the upper glass substrate is formed and an electric signal is lead out from the functional element through the via hole so that the functional element and circuit board are electrically connected (See Japanese Unexamined Patent Publication No. 10-213441).
More specifically, in the small size electronic part, a glass substrate having a via or through hole therein is bonded to a silicon substrate, and conductive paste (or metal) is filled in the through hole, so that an external circuit board is made to be electrically connected to the functional element using the conductive paste.
The aforementioned conventional technique has a drawback that, when the conductive paste is filled in the through hole, air bubbles may be produced in the conductive paste. This causes a problem of contact failure caused by these air bubbles and the reliability is therefore decreased.
In particular, when the communicating hole is made of a small diameter and given that the electronic parts are made small-sized, air bubbles are more likely to be produced, and therefore in order to avoid this the through hole must be made of a larger diameter and accordingly there has been a problem that the part size is increased and the mounting surface increases in size.
Moreover, because the thermal expansion coefficient of the conductive paste is different from that of glass material, when a temperature change is produced in a small size electronic part, there are cases in which cracks occur in the glass substrate.
In order to lead out an electric signal from a functional element reliably, it is possible to provide a conductive film on the internal wall surface of the communicating hole as a substitute for the conductive paste. In this case, however, when a through hole is processed in a glass substrate by sandblasting, chips (broken pieces of glass or their traces) may be produced on the side of the surface of the glass substrate to which a silicon substrate is joined. Because of this, when the surfaces of a silicon substrate and glass substrate are joined, a step-like portion is produced between the silicon substrate and the through hole by the chip. As a result, when a conductive film is processed on the internal wall surface of the through hole, the conductive film may be disconnected by these step-like portions and there is a problem of decreased yields.
The present invention has been made in view of the above problems of the conventional technique, and it is an object of the invention to provide a small size electronic part in which a signal output from a functional element is lead to the outside reliably.
It is also an object of the invention to provide a method for manufacturing such a small size electronic part, as well as a method for forming a via hole for use in such a small size electronic part.
According to the invention, the small size electronic part comprises: a silicon substrate having a functional element and a signal output portion to output a signal from the functional element outside the electronic part; a glass substrate provided on the silicon substrate such that the signal output portion of the silicon substrate is in contact with the glass substrate; a communicating hole provided in the glass substrate and in at least a portion of the signal output portion of the silicon substrate so as to pass through the glass substrate and cut into at least a part of the signal output portion; and a conductive film provided on an inner wall surface of the communicating hole and extending on a surface of the glass substrate.
As constructed this way, the communicating hole is provided so as to pass through the glass substrate and in succession to this be cut into at least a part of the signal output portion, and the conductive film is provided on the internal wall surface of the through hole, and formed so as to extend to the surface side of the glass substrate. The internal wall surface of the communicating hole is continuously provided from the glass substrate to the silicon substrate. Because of this, disconnection of the conductive film caused by chips between the glass substrate and silicon substrate is avoided, and because of this conductive film, the functional element and the outside can be electrically connected through the signal output potion.
The functional element may be sealed by the glass substrate, so that the space for accommodating the functional element can be made substantially a vacuum. Because of this, for example, in a functional element containing a vibrator, the vibrator can be vibrated in a condition so that air resistance applied to the vibrator is reduced.
The communicating hole is preferably formed with a tapered shape so that the diameter is gradually reduced over from the opening side of a glass substrate to a silicon substrate. According to this structure, when the communicating hole is viewed from the opening side of the glass substrate nearly the whole of the internal wall surface can be made exposed, and a conductive film can be easily processed on the internal wall surface of the communicating hole by means of sputtering, etc.
A soldering bump may be provided in a part of a conductive film located on the surface side of the glass substrate. By connecting the soldering bump to an electrode pad, provided on an external circuit board, the functional element can be electrically connected to external equipment.
The functional element may be constructed as a detecting element for detecting external force including angular velocity and acceleration.
The small size electronic part may comprise another glass substrate bonded to a back side of the silicon substrate. According to this structure, the two glass substrates are bonded to the surface side and back side of the silicon substrate, whereby the functional element formed in the silicon substrate can be sealed.
The silicon substrate may comprise an SOI substrate having an insulating film, a first silicon layer in which a functional element and signal output portion are processed and which is provided on the surface side of the insulating film, and a second silicon layer which is provided on the back side of the insulating film, the glass substrate being provided on the surface side of the first silicon layer of the SOI substrate, and a communicating hole is provided in the glass substrate and first silicon layer. In this way, a small size electronic part can be also be constructed using an SOI substrate.
A method of manufacturing a small size electronic part according to the invention comprises a thin portion processing step for processing a thin portion in a silicon substrate by providing a concave groove portion on a first surface of the silicon substrate, a first joining step for joining the surface of a first glass substrate to the surface of the silicon substrate, a functional element processing step for processing a functional element and a signal output portion to output a signal from the functional element to the outside in the thin portion of the silicon substrate, a second joining step for joining the surface of a second glass substrate having an accommodating concave portion comprising a closed space to accommodate the functional element to a second surface of the silicon substrate, a communicating hole processing step for processing a communicating hole provided so as to pass through at least either of the fist and second glass substrate and in succession to this be further cut into at least a part of the signal output portion, and a conductive film processing step for providing a conductive film on the internal wall surface of the through hole.
According to such a manufacturing method of a small size electronic part, first in a thin portion processing step a thin portion is processed by providing a concave groove potion on a first surface of a silicon substrate, next in a first joining step the surfaces of the silicon substrate and a first glass substrate are joined by means of anodic bonding, next in a functional element processing step a functional element and signal output portion are processed in the thin portion and the surface of a second glass substrate is joined to a second surface of the silicon substrate. In addition to this, in a communicating hole processing step, a communicating hole is provided so as to pass through at least either of the first and second glass substrate and in succession to this processed so as to be further cut into at least a part of the signal output portion. Last, in a conductive film processing step on the internal wall surface of the communicating hole, a conductive film electrically connected to the functional element through the signal output portion is provided, for example, by means of sputtering, evaporation, etc.
In this way, as the communicating hole is provided so as to pass through the glass substrate and in succession to this further cut into the silicon substrate after the surfaces of the silicon substrate and glass substrate have been joined, the conductive film will not be disconnected between the glass substrate and silicon substrate and the functional element and the outside can be electrically connected by the conductive film.
A manufacturing method of a small size electronic part according to the invention comprises a concave portion processing step for processing a concave portion on the surface of a first glass substrate, a first joining step for joining a first surface of a silicon substrate to the surface of the first glass substrate having the concave portion, a functional element processing step for processing a functional element in the part of the silicon to cover the concave portion and processing a signal output portion to output a signal from the functional element, a second joining step for joining the surface of a second glass substrate having an accommodating concave portion comprising a closed space to accommodate the functional element to a second surface of the silicon substrate, a communicating hole processing step for processing a communicating hole provided so as to pass through at least either of the first and second glass substrate and in succession to this be further cut into at least a part of the signal output portion, and a conductive film processing step for providing a conductive film on the internal wall surface of the through hole.
According to such a manufacturing method of a small size electronic part, first in a concave portion processing step a concave portion is processed on the surface of a first glass substrate, next in a first joining step a first surface of a silicon substrate is joined to the surface of the first glass substrate, next in a functional element processing step a functional element is processed in a part of the silicon to cover the concave portion and a signal output portion to output a signal from the functional element is processed, and further in a second joining step the surface of a second glass substrate is joined to a second surface the silicon substrate. In addition to this, in a communicating hole processing step a communicating hole provided so as to pass through at least either of the first and second glass substrate and in succession to this be further cut into at least a part of the signal output portion, is processed by, for example, sandblasting. Last, in a conductive film processing step a conductive film electrically connected to the functional element is provided on the internal wall surface of the communicating hole by evaporation means such as, for example, sputtering, etc. Through this conductive film the silicon substrate and the outside can be electrically connected.
A method of manufacturing a small size electronic part according to the invention comprises a functional element processing step for processing a functional element and a signal output portion to output a signal from the functional element to the outside in a first silicon layer of an SOI substrate made up of an insulating film, the first silicon layer provided on the surface side of the insulating film, and a second silicon layer provided on the back side of the insulating film, a joining step for joining the surface of a glass substrate having an accommodating concave portion comprising a closed space to accommodate the functional element to the surface of the first silicon layer of the SOI substrate, a communicating hole processing step for processing a communicating hole provided so as to pass through the glass substrate and in succession to this be further cut into at least a part of the signal output portion, and a conductive film processing step for processing a conductive film on the inner wall surface of the through hole.
According to such a manufacturing method of a small size electronic part, first in a functional element processing step in a first silicon layer of an SOI substrate a functional element and a signal output portion to output a signal from the functional element are processed, and next in a joining step the surface of a glass substrate is joined to the surface of the first silicon layer of the SOI substrate. In addition to this, in a communicating hole processing step, a communicating hole is provided so as to pass through the glass substrate and in succession to this be further cut into at least a part of the signal output portion. In a last conductive film processing step, a conductive film electrically connected to the functional element is provided on the internal wall surface of the through hole, and through this conductive film the silicon substrate and the outside can be electrically connected.
A method of forming a via hole for use in a mall size electronic part according to the invention is also disclosed. The method for forming a via hole for use in a small size electronic part having a functional element and a signal output portion to output a signal from the functional element to the outside comprises a joining step for joining the surfaces of a silicon substrate and glass substrate, a communicating hole processing step for processing a communicating hole provided so as to pass through the glass substrate and in succession to this be further cut into at least a part of the signal output portion, and a conductive film processing step for processing a conductive film on the internal wall surface of the through hole.
According to the method of forming a via hole, first in a communicating hole processing step a communicating in hole is provided so as to pass through a glass substrate and in succession to this be further cut into at least a part of a signal output portion by, for example, sandblasting from the surface side of the glass substrate. Further, in a conductive film processing step, a conductive film electrically connected to a functional element is provided on the internal wall surface of the communicating hole by means of, for example, sputtering, etc., and by this conductive film a silicon substrate and the outside can be electrically connected.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.